题目

已知曲线y=x4+ax2+1在点(-1,a+2)处切线的斜率为8,则a=(  ) A.9                                                             B.6 C.-9                                                          D.-6 答案:D [解析] y′=4x3+2ax,y′|x=-1=-4-2a=8 ∴a=-6.
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